We report on solvation dynamics measurements of the chromophore nile blue i
n ethanol confined to sol-gel glasses with 50 Angstrom and 75 Angstrom aver
age pore size and compare them with the dynamics of the respective bulk sol
ution. Both the amplitude of the dynamic Stokes shift as well as the dynami
cs of the solvation process are drastically changed upon confinement. In bo
th confined solutions the dynamic Stokes shift is reduced by a factor of ab
out 2. As the large majority of the chromophores is adsorbed at the inner p
ore surfaces the solute molecules interact with only a "half-space" of solv
ent molecules. In a first approximation this decreases the stabilization en
ergy by a factor of 2. The solvation dynamics in the confined solutions sho
w nonexponential behavior comparable to the bulk. However, the whole solvat
ion process slows down and the single decay time constants characterizing i
t increase with decreasing pore size of the sol-gel glass. We have introduc
ed two phenomenological models to rationalize this behavior. The enhanced p
olarization field model takes into account the confinement and predicts a s
trengthening of the solvent's polarization field in an extended solvation c
age induced by the electrical field of the chromophore. The steric hindranc
e model focuses on the interaction of the liquid with the surface reducing
molecular mobility resulting in longer relaxation times. Probably both effe
cts are of relevance in the confined solutions investigated. Confinement af
fects the steady-state spectra as well leading to a redshift of the absorpt
ion and a blueshift of the fluorescence. Additional data on the reorientati
onal dynamics of the chromophore are consistent with the fact that the mole
cules are predominantly adsorbed at the pore surfaces. (C) 2001 American In
stitute of Physics.